Simulation process of radiofrequency scenario in radio mobile environment and testing system employing said process

ABSTRACT

A testing system includes simulation equipment for generating a radiofrequency test signal for the receivers of a base transceiver station, which is equipped with an intelligent array antenna having N sensors. The simulation equipment generates a complex signal consisting of N identical radiofrequency signals with differing phases. These signals are conveyed towards N antenna input connectors of the receivers to be tested. The N test signals are obtained by generating as many groups of N digital isofrequential carriers as are required to simulate the directions of a useful signal with an arbitrary number of echoes, and the directions of an arbitrary number of isofrequential interferent carriers. The N carriers of each group are appropriately modulated and digitally multiplied by the same number of relevant beamforming coefficients to produce, within each group, gradually increasing phase values.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/EP98/07762 which has an Internationalfiling date of Nov. 26, 1998, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to the field of test systems fortelecommunication equipment and more in particular to a radiofrequencyscenario simulation process in mobile radio environment for the testingof receivers of base transceiver stations with intelligent antennas, andtesting system employing said process.

Before introducing the art known in the field of the invention, it isnecessary to briefly describe the operation and problems related to theuse of the so-called “intelligent” antennas; to justify, in theapplicant's opinion, the lack of testing systems oriented to such a kindof antennas.

As it is already known, the use of intelligent antennas commences in themobile radio environment to render the reutilization of the same carrierfrequencies in cells of adjacent clusters less critical. This criticalcharacter is particularly evident in high traffic urban environment,where reutilization distances can suffer a considerable reduction due tothe reduced dimensions of the cells, often of some hundreds of metersonly. The use of traditional omnidirectional antennas, or oftrisectorial ones, involves high interference problems in theseparticular environments by isofrequential signals coming from adjacentclusters. This is due to the scarce directivity of the antennas, whichconsequently involves the transmission of comparatively high powersignals by the base transceiver stations (BTS). On the contrary, theintelligent array antenna, is a directive radiant system, able toconcentrate the electromagnetic field in the original estimateddirection of the signal transmitted by a generic mobile MS (in all thedirections of the azimuth plane), separately for all the mobiles of acell where the antenna is allocated. The antenna is thereforecharacterized by dynamic radiation diagrams (as many as are the timedivision carriers assigned to the BTS multiplied by the number of timeslots) fit with main lobes of reduced angular opening that follow up thedirections of the relevant mobiles, thus avoiding to vainly leak powerout of these directions. Reciprocally in reception, this involves areduction of the total level of isofrequential interferents and,consequently, of the reutilization distance of the same carriers, andtherefore of the dimensions of clusters.

It is also known that the intelligent antennas are based on the use ofelectromagnetic field sensor arrays, each sensor being connected to itsown transceiver, and the whole of transceivers to a process module ableto duly process the signals received, or transmitted, by the singlesensors. Usually, the receiver acts as “master”, that is, it estimateson the azimuth plane the arrival directions of signals of the mobiles intransit in its cell and communicates this information to the transmitterthat synthesises the angular openings of the antennas in the abovementioned angular directions, supplying the single sensors with replicasof a same signal, duly phase shifted among them.

While for the transmitter associated to an intelligent array antennathere is no particular realization problem, the same is not true for theimplementation of the similar receiver, since the estimate of thearrival directions of useful signals is a complex operation from thecomputation point of view. It requires in fact an opportune processingof the module and phase information of more replicas of the radio signalreceived by the different sensors of the array. Said complexity derivesfrom the fact to distinguish in the signal transduced from the array,the directions of the useful signals from those of relevant interferentsignals, that is the isofrequential signals emitted by mobilestransiting in adjacent cluster cells, and the echoes due to the multiplereflections of the useful by obstacles spread over the territory, whoseextent and time delay depend on the geographic environment of the cell(urban, suburban, rural environment). This information on the arrivaldirections is then used by the receiver to perform a spatial filteringof the N signals transduced by the array, in order to filter the usefulfrom the different interferents.

BACKGROUND ART

In the examples of base transceiver stations with intelligent antennasaccording to the known art, a similar discrimination of the useful fromthe interferents is only partially made. This does not happen for anewly conceived base transceiver station, implemented by the sameapplicant, whose main innovative aspects have been protected by thefollowing relevant patent applications:

-   EP 0 878 974 under the title “Communication Method for cellular    telephone systems”, filed on May 16, 1997;-   WO 99/33141 under the title “Discrimination process of a useful    signal by a plurality of isofrequential interferent signals received    by array antennas of base transceiver stations for cellular    telecommunication and relevant method”.

In particular, the last mentioned application solves the problem ofdiscrimination of the useful signal from a plurality of isofrequentialinterferents through a spatial filtering method, or beamforming, made onsignals transduced by the array, previously submitted to a processingdetermining the number and the arrival directions of the waves incisingon the array, distinguishing the useful from the relevant interferents.

Therefore, it is evident that in testing systems of base transceiverstations equipped with intelligent antenna, of old conception, theproblem to simulate a radiofrequency scenario reflecting as precisely aspossible what actually occurs in the reality, is not particularlyperceived. This is a consequence of the fact that the beamformingalgorithms there used do not discriminate (or do it in a rough andpredictable manner) the useful signals from the relevant interferentechoes. It is then possible, and in the practice it generally occurs inthe context of the known art, to use the old test equipment for receiverapparatus of the base transceiver stations, with omnidirectional ortrisectorial antennas, apart from the simulation of the arrivaldirections of useful and relevant interfering echoes. Consequently, theactual test of the behaviour of the receiver complete with intelligentarray antenna requires opportune test transmitters located, ad hoc, onthe territory.

U.S. Pat. No. 5,539,772 is an example of a test equipment designed forverifies the performance of a digital satellite receiver belonging to amobile terminal unit. As known, a geostationary satellite retransmitstowards the mobile a phone call received from a satellite groundstation, in turn connected to a public telephone network. The relevantclaim 1 of the citation discloses an Apparatus for verifying performanceof a RF receiver, comprising:

-   -   arbitrary waveform generator means for outputting an analog        in-phase waveform and an analog quadrature waveform in        accordance with sampled digital waveform data, said arbitrary        waveform generator means including parallel first and second        First-In-First-Out random access memories for storing the        sampled digital waveform data;    -   the sampled digital waveform data comprising an in-phase        waveform file stored in said First-In-First-Out memory and a        quadrature waveform file stored in said second        First-In-First-Out memory    -   each of the in-phase and quadrature waveform files including 60%        root-cosine differential quadrature phase shift keyed data        corresponding to successive frames of primary transmission        channel data, co-channel interference data, adjacent channel        interference data, and data relating to at least one of a        plurality of impairments;    -   unity gain reconstruction filter means, connected to said        arbitrary waveform generator means, for smoothing the analog        in-phase and quadrature waveforms    -   vector signal generator means, responsive to the filtered analog        in-phase and quadrature waveforms, for outputting a modulated RF        signal; and    -   means for coupling an input of the RF receiver to the modulated        RF signal output from said vector signal generator.

A further independent claim of the same cited prior art is directed to amethod for testing the receiver. In accordance with the claimed method adigital frame including a portion dedicated to reproduce the signaltransmitted, via satellite, to a mobile telephone unit is generated.Except for the framed digital signal, the claimed method has thesubstantial features of the claimed apparatus. In the supportingdescription all the means involved in claim 1 generates a narrow bandtest signal, which because a mobile telephone unit activates only atelephone call at a time, contrarily to the base station which activatesa plurality of simultaneous calls. Accordingly, the signal generated bythe test apparatus of the citation is unsuitable to test a base station,where a suitable test signal should be of the multicarrier type. In theparticular case of GSM with beamforming, a minimal realistic testapparatus is charged to synthesize a useful signal freely displaceableinside a wide radiofrequency band, i.e. the 880–915 MHz for extendedGSM, plus one or more co-channel interferent having a presettabledirection out of 360°. A more versatile apparatus could generate severalsets of similar signals at the various frequencies. No suggestion isgiven in the citation about the design of such a test apparatus.

SUMMARY OF THE INVENTION

A general object of the present invention is to propose a simulationprocess of radiofrequency scenario for the testing of radio receiverswith intelligent array antenna, able to identify the direction of auseful signal from those of isofrequential interferents, irrespective ofthe fact that a spatial filtering is then made.

Elective object of the present invention is that to overcome thedrawbacks of testing systems for receivers of base transceiver stationsof cellular telephone systems of old design, and to propose aradiofrequency scenario simulation process in mobile radio environmentfor the testing of radio receivers of base transceiver stations withintelligent antennas, of new generation, as much realistic as possible,for the whole typology of signals which can incise on the antenna, thatis: the useful signals emitted by several mobiles, the relevant echoesdue to multiple reflections, the isofrequential interferents due to thereutilization of the carriers, the echoes of said interferents, theinterferents from adjacent channel, the echoes of said interferents.

-   a) To attain these objects, scope of the present invention is a    simulation process of radiofrequency scenario, in particular for the    testing of receivers for N sensor intelligent array antennas, as    described in claim 1.

Profitably, the subject process can be used for the simulation of aradiofrequency scenario of any cellular telephone system, characterizedby the reutilization of carriers. The simulated scenario can be tailoredin the way time by time considered more adequate to a particular testingrequirement.

According to another aspect of the invention, the simulated scenario hasdynamic characteristics, obtained varying at pre-set time intervals thesetting of parameters relevant to characteristic magnitudes of usefuland interferent carriers contained in said tables, which define thesimulated scenario, such as for instance: level, delay, arrivaldirection, etc., the duration of said intervals being rather short to becomparable to the time slot employed by similar variations whenoccurring in a real scenario, but however sufficient to thereprogramming of the different phases of the simulated scenario.

Profitably, the simulation of the scenario includes the presence ofnoise, the doppler effect due to the speed of mobiles and the quick andsudden fadings of the electromagnetic field received, caused bydestructive interference from multiple paths (fading of Rayleigh) ormasking by obstacles of different nature encountered by the mobiles.

Since the intelligence of the receivers of a base station for mobileradio systems with intelligent antenna of new generation has thecharacteristics mentioned above, it results that the testing of theseintelligent characteristics requires an adequate stimulation by thetesting system, which shall be able to reproduce a radiofrequencyscenario so richly diversified.

Therefore, further object of the invention is a testing system ofreceivers of a base station per mobile radio systems with intelligentarray antenna, of new generation, employing the scenario simulationprocess scope of the present invention, as described in claim 11.

The great advantage that a similar system has, is to enable a completeand accurate testing of the receivers of the above mentioned basestation, without the need of preparing sample transmitters on theterritory. The system is also characterized by an exceptionalflexibility in preparing the scenario considered time by time moresuitable to the verification of the receiver performance compared to aparticular specification standard. In fact, it is sufficient that thetesting operator fills in a limited number of tables describing thescenario to simulate, afterwards, simply clicking with the mouse thesame become operative in real time.

BRIEF DESCRIPTION OF DRAWINGS

The invention, together with further objects and advantages thereof, maybe understood making reference to the following detailed description,taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a quite general block diagram of the testing system scopeof the present invention, connected to a device to be tested (D.U.T.);

FIG. 2 shows more in detail a SIM_(—)RF block of FIG. 1 belonging to theabove mentioned testing system;

FIG. 3 shows the SIM_(—)RF block of FIG. 2 with higher detail, up to theindication of the single circuit blocks;

FIG. 4 gives a representation of the directions of plane waves incisingon an array antenna, usually employed during the actual operation by thedevice to be tested (DUT) of FIG. 1;

FIG. 5 shows the progressive phase shifting existing among thecomponents of a plane wave front coming from a direction φ of FIG. 4, onthe moment the same incises on the sensors of the array;

FIG. 6 shows a picture on the complex I/Q plane of the rotating vectorsthat represent the components of the plane wave front of FIG. 5; and

FIG. 7 shows the tables previously stored in the permanent storage ofthe processor of FIG. 1, available to the testing operator for thesetting of the parameters distinguishing a scenario to be simulated.

DETAILED DESCRIPTION

Making reference to FIG. 1, it can be noticed a testing system of adevice DUT (Device Under Test) consisting of a simulation equipmentSIM_(—)RF connected to a control processor CNTR_(—)PC through a serialbus ET_(—)LAN of a local network, for instance of the Ethernet type, towhich also the DUT device is connected.

The SIM_(—)RF block has N radiofrequency outputs out1, out,2, . . . ,outN connected, through N coaxial cables, to a same number of inputsin1, in2, . . . , in N of the DUT block. Relevant radiofrequency signalsRF1, RF2, . . . , RFN coming out from the SIM_(—)RF block run along saidcables, and enter the DUT block. Blocks SIM_(—)RF and DUT, as well asthe personal computer CNTR_(—)PC, are connected to the serial busET_(—)LAN. More in particular, the personal computer CNTR_(—)PC isconnected to the ET_(—)LAN bus through its own serial bus SER_(—)PC, theDUT block through a serial bus SER_(—)DUT, and block SIM_(—)RF through Mserial buses SER_(—)PR1, SER_(—)PR2, . . . , SER_(—)PRM and a M+1-thserial bus SER_(—)LO.

In operation, the SIM_(—)RF block is a simulation equipment governed bythe personal computer CNTR_(—)PC, and the DUT block is a receiver of abase transceiver station (BTS) for cellular telephone system of theFDMA/TDMA type, for instance GSM 900 MHz, or DCS 1800 MHz. The whole ofthe RF1, . . . , RFN signals conforms to the selected standard thatdefines the radio interface. Even if not shown in the figure, the abovementioned blocks include one or more interface devices towards the localnetwork ET_(—)LAN.

Observing the testing configuration of the figure (test bed), we canperceive the great advantage offered by the connection in local networkboth of the testing system CNTR_(—)PC, SIM_(—)RF and of the device totest DUT. In fact, this last could send the results of the differenttests directly to the computer CNTR_(—)PC, in a completely asynchronousmode versus the flow of testing data. The control processor will availof evaluation procedures and print of the results, and in the case ofvariation of input stimulations. In this way the testing will resultcompletely automated.

Making reference to FIG. 2, we notice that the simulation equipmentSIM_(—)RF includes M processor modules TX_(—)PROC1, TX_(—)PROC2, . . . ,TX_(—)PROCM; N broad band radiofrequency transmitters WB_(—)TX1,WB_(—)TX2, . . . , WB_(—)TXN; and a LO_(—)CORP block generating Nidentical signals of local oscillator OL, reaching the transmittersWB_(—)TX1, . . . , WB_(—)TXN.

Each TX_(—)PROC block has N outputs for a same number of digitalsequential words Cx_(y) reaching the relevant N parallel buses BS1, BS2,. . . , BSN, where the value of index x indicates the origin from arelevant processor module m-th, while the value of index y indicates then-th bus reached by the signal Cx_(y). I bus BS1, BS2, . . . , BSN areconnected to an input of relevant broad band transmitters WB_(—)TX1,WB_(—)TX2, . . . , WB_(—)TXN identified by the same ordinal number.

In the operation, the architecture of the SIM_(—)RF equipment shows amodularity per time division radio carrier, with a maximum of M carriersgenerated by M modules TX_(—)PROC, and per antenna element, with amaximum of N elements (virtual), supplied by a same number of signalscoming out from the WB_(—)TX transmitters. Each module TX_(—)PROCgenerates also the N-1 replicas of its own carrier, duly phase shifted,necessary to control the modularity per antenna element (virtual).

The processor modules TX_(—)PROC perform the following operations, in acompletely digital manner:

-   acquisition of control signals by the processor CNTR_(—)PC, as    serial messages withdrawn from the bus ET_(—)LAN;-   generation of P numeric isofrequential carriers and GMSK modulation    of the same using an identical modulating signal, obtaining    components in phase I and in quadrature Q of each carrier;-   multiplication of the samples of said components I and Q by relevant    complex constants coming from CNTR_(—)PC, originating “weighed”    components in phase and module in order to realize beamforming, as    we shall see below;-   vectorial sum of I and Q “weighed” components of each carrier,    obtaining in change digital modulated carriers GMSK;-   level control of the above mentioned modulated carriers in steps of    programmable amplitude;-   control of the ramp-up and ramp-down time of the envelope of the    modulated signal, at the beginning and at the end of each burst,    respectively (ramp-up and ramp-down functions);-   numeric conversion at intermediate frequency of each modulated    carrier, obtaining said digital words Cx_(y);-   construction of N transmission digital signals of the multicarrier    type at intermediate frequency, identified IF1, IF2, . . . , IFN,    respectively, coinciding with the buses BS1, BS2, . . . , BSN,    through sum of each m-th word Cx_(y) identified by the same index y.

Signals IF1, IF2, . . . , IFN reaching the N broad band transmittersWB_(—)TX1, WB_(—)TX2, . . . , WB_(—)TXN, are converted to analogue bythe same, typically compensating the distortion of the senx/x type,broad band filtered, and then converted at radiofrequency in testsignals RF1, RF2, . . . , RFN placed in a selected transmissionsub-band. The N signals RF1, RF2, . . . , RFN, thanks to thebeamforming, are suitable to simulate up to M different arrivaldirections from a unique spatial point. The same directions are in factrecognized by the receiver DUT per intelligent antenna of a BTS intesting phase, and therefore without antenna, on the basis of thereciprocal phase shifting existing between the N carriers of each of theM groups of N isofrequential carriers forming the N broad band signalsRF1, RF2, . . . , RFN, globally conveyed in the DUT block by a samenumber of coaxial cables.

FIG. 3 highlights with higher circuit detail what already said in thecomment of FIG. 2; in particular it is supplied the architecture ofprocessor modules TX_(—)PROC and of transmitters WB_(—)TX.

Making reference to FIG. 3, in which the same elements of the previousfigures are indicated with the same symbols, we notice the processormodules TX_(—)PROC1, TX_(—)PROC2, . . . , TX_(—)PROCM of which, only formodule TX_(—)PROC1, the internal architecture is highlighted, being thearchitecture of the remaining modules identical to the highlighted one.The TX_(—)PROC1 module includes N modulators GMSK1, GMSK2, . . . , GMSKNand a INTF_(—)PC block connected, through the serial bus SER_(—)PR1, tothe serial bus ET_(—)LAN of the local network to which all the remainingblocks TX_(—)PROC are abutted, the LO_(—)CORP block, as well as thepersonal computer CNTR_(—)PC and the DUT block highlighted in thetesting configuration (test bed) of FIG. 1. At output of the INTF_(—)PCblock, digital signals are present, indicated as follows:

-   SIM_(—)D, BT_(—)SIM, and SIM_(—)DEL directed towards all the GMSK    modulators;-   N complex data SIM_(—)BEAM_(—)W1, SIM_(—)BEAM_(—)W2, . . . ,    SIM_(—)BEAM_(—)WN addressed towards an input of relevant first    complex digital multipliers M1, M2, . . . , MN, the other input of    which is reached by the components I and Q coming out from relevant    GMSK modulators; and finally-   N identical digital carriers SIM_(—)NCO addressed towards an input    of relevant second digital multipliers MM1, MM2, . . . , MMN, the    other input of which is reached by the signals coming out from    relevant first multipliers M1, M2, . . . , MN (through the adders of    the “weighed” I and Q components, omitted for briefness sake in the    figure).

One clock input of GMSK modulators is reached also by a signal CK, usedfor the generation of relevant and identical digital carriers in baseband.

At the output of the second multipliers MM1, MM2, . . . , MMN the Nsignals C1 ₁, C1 ₂, . . . , C1 _(N) of FIG. 2 are present; these lastreach a first input of relevant N digital adders 1, 2, . . . , N, havingtwo inputs, also included in the TX_(—)PROC1 block. The second input ofsaid adders is reached by relevant sum signals of corresponding signalsCx_(y) generated by the remaining modules TX_(—)PROC of the blockSIM_(—)RF. As it can be noticed in the figure, TX_(—)PROC blocks areplaced in cascade as for the adders 1 . . . N, that is the output of ageneric adder of a block reaches an input of the corresponding adder ofthe block placed downstream. Consequently, adders 1, 2, . . . , N of theTX_(—)PROC1 block, placed downstream the whole chain of blocksTX_(—)PROC, obtain at output the digital signals at intermediatefrequency IF1, IF2, . . . , IFN, as cumulative sum of relevant signalsCx_(y) corresponding to those indicated on buses BS1, BS2, . . . , BSNof FIG. 2. It results that the implementation of these last is actuallyobtained through the M groups of adders 1, 2, . . . , N placed incascade.

The N digital signals at intermediate frequency IF1, IF2, . . . , IFNreach a same number of digital/analogue converters included in therelevant blocks WB_(—)TX₁, WB_(—)TX2, . . . , WB_(—)TXN. Convertedsignals are duly broad band filtered, amplified, and sent to a firstinput of relevant mixers MX1, MX2, . . . , MXN, reached also by the Nidentical signals of local oscillator OL coming from LO_(—)CORP,obtaining at output N radiofrequency signals. These last are dulyfiltered and sent to relevant power amplifiers PA1, PA2, . . . , PAN,obtaining the N signals RF1, RF2, . . . , RFN present at the outputsout1, out2, . . . , outN of SIM_(—)RF.

All what said up to now concerning the operation of the SIM_(—)RFequipment of FIGS. 2 and 3 relates to what happens in a single timeslot. This time (577 μs) is too short to complete the dialogue betweenCNTR_(—)PC and SIM_(—)RF and the required programming of modulators GMSKby the INTF_(—)PC block; consequently the settings of the SIM_(—)RFequipment, for all the time slot of the present frame possibly involved,shall be made during a frame time (4,61 ms) and shall become operativeduring the subsequent GSM frame.

Continuing the description of the operation of the simulation equipmentSIM_(—)RF, it is impossible to leave out of consideration the dialoguebetween this last and the control personal computer CNTR_(—)PC. Beforedescribing the methods of such a dialogue it is useful to give sometheoretical clarifications on the beamforming, used in the presentinvention to simulate the arrival direction of useful and interferents.

Making reference to FIG. 4, we notice an array antenna, seen from thetop, consisting of N sensors a1, a2, a3, . . . , aN aligned along astraight line and separated one from the other of a distance d=λ/2, atcentreband frequency of the band assigned by the particular transmissionstandard valid for the type of BTS to be tested. The antenna has a planeform, whose trace on the figure plane corresponds to the sensorsjunction line. The antenna plane is stricken by two plane waves p1 andp2 coming from two different directions, indicated with two straightlines, perpendicular to the relevant wave fronts and forming tworelevant arrival angles φ and θ with the trace of the antenna plane.

Making reference to FIG. 5, we notice the wave front p1 on the moment itstrikes the sensor a1 placed at one end of the array. From the figure itis clear that the subsequent sensors shall be stricken with everincreasing delays, consequently the modulated carrier corresponding tothe plane wave p1 shall be seen at the input of the different sensors ofthe array like N identical modulated carriers s1(t), s2(t), . . . ,sN(t), phase shifted among them by ever increasing angles. All thesephase shiftings are therefore in biunivocal relation with the arrivaldirection of p1, so that to estimate the unknown arrival direction of ageneric carrier coming from a mobile, it is sufficient to measure thereciprocal phase shiftings among the signals received from singlesensors, taking an ending one to determine an absolute phase reference.This is just what the block DUT performs in its actual operation.Concerning the simulation equipment SIM_(—)RF, the dual reasoningapplies, that is, starting from a direction to simulate of a testcarrier, it is necessary to calculate some complex constants(beamforming coefficients) which, multiplied by N identical modulatedcarriers p1 give the reciprocal phase shiftings identical to those ofthe wave front of FIG. 5. It is then clear that sending this set ofcarriers directly downstream the array, excluding this last, we obtainthe same effect as that obtained sending a carrier from a direction φwith inserted antenna. The reasoning made for the carrier p1, whosearrival direction has to be simulated, applies to any other carrier,both useful or interferent, whose directions must be simulated them too.It is this possible to test from a unique spatial point, the laboratoryone, through a simulated scenario, the characteristics of the receiverdefining the intelligent behaviour of the same.

Referring to FIGS. 5 and 6, it is now described the calculation ofbeamforming coefficients enabling to obtain the set of phase shiftedcarriers as desired. To this purpose, it is used in FIG. 6 a vectorialrepresentation on plane 1, Q of the modulated carriers s1(t), s2(t), . .. , sN(t) of FIG. 5 present at the input of the single sensors a1, a2,a3, . . . , aN, indicating the corresponding rotating vectors con S₁,S₂, S₃, . . . , S_(N). The phase absolute reference is selectedarbitrarily assuming equal to zero the phase of vector S₁. Indicatingthe vectors in exponential form with module A, and letting Ψ=π cos φ,the following representation applies:

S₁=Ae^(j0) $\begin{matrix}{S_{2} = {{A\;{\mathbb{e}}^{j\frac{2\pi}{\lambda}d\mspace{11mu}\cos\mspace{11mu}\varphi}} = {{A\;{\mathbb{e}}^{{j\pi}\mspace{11mu}\cos\mspace{11mu}\varphi}} = {A\;{\mathbb{e}}^{j\Psi}}}}} \\{S_{3} = {{A\;{\mathbb{e}}^{j\frac{2\pi}{\lambda}d\mspace{11mu}\cos\mspace{11mu}\varphi}} = {{A\;{\mathbb{e}}^{{j2\pi}\mspace{11mu}\cos\mspace{11mu}\varphi}} = {A\;{\mathbb{e}}^{j2\Psi}}}}}\end{matrix}$$S_{N} = {{A\;{\mathbb{e}}^{j\frac{2\pi}{\lambda}{({N - 1})}d\mspace{11mu}\cos\mspace{11mu}\varphi}} = {{A\;{\mathbb{e}}^{{{j{({N - 1})}}\pi\mspace{11mu}\cos\mspace{11mu}\varphi}\;}} = {A\;{\mathbb{e}}^{{j{({N - 1})}}\Psi}}}}$

The calculation of the Cartesian components of each vector is nowimmediate, according to the known trigonometric relations:Q₁=AI₁=0Q₂ =A cos(Ψ)=A cos(π cos φ)I ₂ =A sin(Ψ)=A sin(π cos φ)Q ₃ =A cos(2Ψ)=A cos(2π cos φ)I ₃ =A sin(2Ψ)=A sin(2π cos φ)Q _(N) =A cos((N−1))=A cos((N−1)π cos φ)I _(N) =A sin((N−1)Ψ)=A sin((N−1)π cos φ)

The N pairs of values I and Q so obtained correspond to beamformingcoefficients SIM_(—)BEAM_(—)W1, SIM_(—)BEAM_(—)W2, . . . ,SIM_(—)BEAM_(—)WN of FIG. 3. In the example considered, the mathematicalprocess described above must be repeated for the calculation ofbeamforming coefficients of the carrier p2; in general, M procedure foreach one of the M modulated carriers, generated by the SIM_(—)RFequipment have to be made.

It is now described the dialogue method between the personal computerCNTR_(—)PC and the simulation equipment SIM_(—)RF, in order to betterhighlight the functions of the INTF_(—)PC block of FIG. 3, missing inthe mentioned known art. The above mentioned dialogue occurs throughsending of messages from CNTR_(—)PC directly towards the TX_(—)PROCunits; each message is transmitted in series with a label specifying theaddress of the TX_(—)PROC addressee unit and the length of theassociated message, immediately followed by the message content, that isthe true data.

Making reference to FIG. 7, messages are automatically prepared by theprocessor CNTR_(—)PC, after the testing operator has filled in a limitednumber of predetermined tables TAB.1, TAB.2, . . . , TAB.K, whichsummarize the general data describing the scenario to simulate. Theselection of data to enter can determine the opening of submenuscontaining the parameters to select for the option specified. Thetabular display of SIM_(—)RF setting data is made through windowsselectable on the screen and connected among them, meaning that themodification of one or more data will affect in real time all thewindows involved in said data. Clicking with the mouse, the operatoropens a list of possible selectable values, for each case of the table.The operator can retrieve the tables at any moment during the testingand the possible updatings are operational in real time.

For a better comprehension of the fields given in tables of FIG. 7, ofthose that shall be included in subsequent subtables of the relevantsubmenus, and of those of additional tables which will clarify thecontent of the messages correspondingly generated, it is helpful to givejust from now some brief preliminary notions on the fundamental aspectsthat define the radio Um interface of the system GSM, 900 MHz, to whichthe testing system and the device to be tested of the example shown inFIG. 1, make explicit reference. From these notions some operationspecifications for the testing system of FIG. 1 will derive. As itresults from the recommendations on this purpose:

-   each BTS employs one or more radio carriers, each one allocated in    the 900 MHz band (TX BTS: 925–960 MHz; TX MS: 880–915 MHz);-   a carrier BCCH (broadcast carrier) for the transmission, is    associated to each cell, diffused to all the mobiles, of the cell    characteristic information;-   each radio carrier is time divided in time slots of about 577 μs    each, the transmission takes place in digital way with bit duration    of about 3.6 μs;-   each time slot contains a Normal Burst of 148 bit, or an Access    Burst of 88 bit;-   each Normal Burst contains a 26 bit synchronization sequence    (Training sequence or middambolo), temporally positioned at the    burst centre;-   the repeatitivity of the time slot occurs at frame interval of about    4.61 ms, for 8 time slot frames (TS0 . . . TS7);-   26 sequential frames are organized in a 120 ms multiframe; 51    sequential multiframes are organized in a 6,12 second superframe;    2048 sequential superframes are organized within an iperframe of    approximately three hours and a half; such a subdivision is useful    to synchronise events requiring long real times to be acquired and    processed;-   the power emitted by the BTS on each time slot of each radio carrier    has a level (Emission Level) depending on the distance separating    BTS from MS (said distance is evaluated on the basis of the TIMING    ADVANCE parameter), and level and quality of the signal received.

From the above mentioned specifications it can be noticed that up tonow, recommendations concerning the behaviour of the intelligent antennado not exist.

The BTS controls the radio interface monitoring the following parameters(updated every 480 ms):

-   distance of MS from BTS, proportional to the radio signal    propagation time (parameter: TIMING ADVANCE);-   level of the signal received, depending on the attenuation of radio    length separating MS from BTS, within the coverage along a specified    direction (parameter: RX_(—)LEV);-   useful/interferent ratio C/I, depending on the above mentioned    considerations and essentially deriving from the concept of radio    resources reutilization (RX_(—)QUAL parameter).

Based on the general notions mentioned above, some operationspecifications result for the testing system of FIG. 1 that, as it isremembered, consists of the simulation equipment SIM_(—)RF connected toits own control processor CNTR_(—)PC through a serial bus ET_(—)LAN of alocal network. The above mentioned specifications are given below:

standard of the radio interface EGSM900 subdivision in 10 MHz sub-bandsTX 875–885 MHz (because a wide band digital transmitter 885–895 MHz ableto cover the whole band cannot be 895–905 MHz realized up to now)905–915 MHz Power rated level TX for carrier −13 dBm at the output ofeach WB_(—)TX digital control TX power level 15 steps, 1 dB each (forchannel) Number of antenna elements TX N = 8 Maximum number of RFcarriers M = 16 No. of time slots actually assigned Set possibility foreach carrier simulation of movement for each Speed setting possible RFcarrier (3 ÷ 250 km/h) relative delays between RF carriers programmablewith 1 bit GSM resolution (156 bit max) relative delays between echoesof the programmable with 50 ns same carrier resolution (3.6 μs max)simulation of angular direction programmable on 360° with 1° (for eachRF carrier) resolution

Going back now to the general tables of FIG. 7, we can notice that agiven number K is foreseen (only two of them are described in detail)each one referred to a subsequent GSM frame having 4.61 ms duration.This strategy enables to gradually vary the parameters of the simulatedscenario, going close to what occurs in the dynamics of a real scenario.In fact, it is known that the algorithms used by a BTS to acquire themain merit parameters of the receiver require times longer than that ofa single frame. Furthermore, in the case of receiver for intelligentantenna, like that of block DUT of FIG. 1, the same works with adaptivealgorithms performing their function at best on several subsequentframes. La sequence of K tables is cyclically repeated to enable acontinuous operation of the testing system. The cyclic repetition oftests enables the results of the measures to reach a permanent steadycondition after each manual updating of one or more parameters of thescenario, and demonstrates to be useful for a statistical evaluation ofresults. The transformation methods of the information included intables of FIG. 7 in messages for the SIM_(—)RF equipment shall bedescribed hereafter.

The items indicated in the different cases of the general tables of FIG.7 are self-explanatory and do not require additional comments.Concerning the connection of the general tables to submenus, the choice“FREQUENCY HOPPING: YES” determines the opening of a submenu with thefollowing parameters to set:

PARAMETER IDENTIFICATION RANGE N° channels RF available N 1 . . . 50 N°selected hopping sequence HSN 0 . . . 63 offset of the allocation indexof MS MAIO 0 . . . N-1

The option “FADING: NO” does not determine opening of any submenu.

The option “FADING: YES” determines the opening of a submenu for theselection of one of the following known propagation models:

PROPAGATION MODEL IDENTIFICATION rural area RAx (6 taps) hilly terrainHTx (12 taps) reduced hilly terrain HTx (6 taps) urban area TUx (12taps) reduced urban area TUx (6 taps) equalization test EQx (6 taps)arbitrary CUSTOM

The selection of any propagation model (excluding CUSTOM) imposes thevalues of “RF level”, “delay” and “Doppler spectrum type” of the tableof FIG. 7, which determined this choice. Access to the columns of theabove mentioned table is therefore inhibited to the operator, and thevalues automatically included in these columns are those defined byspecifications GSM 05.05 Annex C (Propagation conditions). Furthermore,rural area models, reduced hilly terrain, reduced urban area,equalization test automatically engage 6 carriers of SIM_(—)RF; thehilly terrain, urban area models automatically engage 12 carriers ofSIM_(—)RF. The selection of the discretionary model (CUSTOM) determinesthe enabling of the columns “delay” and “Doppler spectrum type” and theengagement of one sole RF carrier, since the selection of the number andcharacteristics of possible echoes and of the possible (taps) of themodel itself is up to the operator.

Once the tables of FIG. 7 are filled in with the data for thesimulation, guided in this by the relevant submenus, the processorCNTR_(—)PC generates the messages instructing the processor modulesTX_(—)PROC1, TX_(—)PROC2, . . . , TX_(—)PROCM and the block LO_(—)CORP.

The following table lists the identification names of messages and therelevant addressee units:

Bit PC→ PC→ TYPE OF MESSAGE No. TX_(—)PROC LO_(—)CORP SIM_(—)NCO (1 . .. 16) 8 x SIM_(—)D (1 . . . 16) 116 x SIM_(—)BEAM Wn (1 . . . 16) 256 xSIM_(—)DEL (1 . . . 16) 16 x BT_(—)SIM 8 x P_(—)SYNT_(—)SIM 8 x TSN 8 x

All the messages having suffix (1 . . . 16) are intended as separatemessages sent to the TX_(—)PROCm module relevant to the carrier m-th (m1 to 16). Concerning the SIM_(—)BEAM_(—)Wn messages, the suffix n variesfrom 1 to N=8 coinciding with a generic value m to indicate N separatemessages sent to the same module TX_(—)PROCm.

The following table gives the meaning of the messages listed in theprevious table:

NAME Bit No. MEANING SIM_(—)NCO 16 Programming of the RF channeltransmitted in uplink SIM_(—)D 116 data to be transmitted in uplink(modulating signal) SIM_(—)BEAM_(—)Wn 256 Module and phase ofbeamforming coefficients SIM_(—)DEL 16 delay of the simulated carrier inuplink BT_(—)SIM 8 training sequence code, TSC (3 bit) + selectionbetween NORMAL or ACCESS burst (1 bit) P_(—)SYNT_(—)SIM 256 programmingof LO_(—)CORP for the selection of the carrier in the assigned time slotTSN 8 number of the time slot of the GSM frame (TSN = 0 . . . 7)

The necessary procedures to process data supplied by the user and toobtain the information message in the serial format accepted by thenetwork ET_(—)LAN and by interface blocks INTF_(—)PC of the simulationequipment SIM_(—)RF are developed on CNTR_(—)PC. Following is the listof the above mentioned procedures, specifying the procedure inputinformation (inputs) and the information supplied by the procedureitself (outputs). The inputs are the parameters selected by the user andentered through menu and submenus. The outputs contain the messagestransferred by CNTR_(—)PC, via bus ET_(—)LAN, to modules TX_(—)PROC andLO_(—)CORP.

The procedures performed by CNTR_(—)PC for the generation of the abovementioned messages are the following:

-   frequency hopping algorithm (see spec. GSM 05.03)-   inputs: N,HSN,MAIO    outputs: RF channel number;-   beamforming algorithm (see the previous representation of FIGS. 4, 5    and 6)-   inputs: arrival angle    outputs: beamforming coefficients;-   RF scenario simulation (see spec. GSM 05.05 Annex C, propagation    condition)-   inputs: standard propagation model, MS speed    outputs: sequence of amplitude multiplication coefficients (one per    frame); relative delays between echoes of the same carrier.

Making reference to FIG. 3, we can notice that a great part of thecontent of messages transferred by CNTR_(—)PC, via ET_(—)LAN, to theinterface circuit INTF_(—)PC, are in their turn transferred to usingdevices. This occurs for the contents of the messages SIM_(—)D, TSN andSIM_(—)DEL, transferred to modulators GMSK; for the contents of themessages SIM_(—)BEAM_(—)Wn, transferred to first multipliers M1, M2, . .. , MN; and for the content of the message SIM_(—)NCO, transferred tothe second multipliers MM1, MM2, . . . , MMN.

The contents of all the messages are updated by CNTR_(—)PC at each 4.61ms GSM frame, and sent according to the same intervals to the concernedunits placed in local network, even if the content of a message isunchanged compared to that of the preceding frame. Consequently theconcerned modules TX_(—)PROC and LO_(—)CORP, can process in a frame timethe updated contents of the relevant messages, in order to be able tochange in real time the simulated magnitudes relevant to the modulatedcarriers sent to the DUT block of FIG. 1 in the subsequent frame.

The updating of the message content made by CNTR_(—)PC of FIG. 1 at eachframe, in absence of modifications introduced by the testing operator inthe contents of the sequence of K tables of FIG. 7, and of subtablesassociated to the same, shall be that imposed by said sequence. On thecontrary, in presence of modifications, it will reflect that of theupdated sequence, starting from the point in the recurrent cycle inwhich the same is rendered operative. For a better understanding of theupdating dynamics of messages generated by CNTR_(—)PC, it is appropriateto underline that the compilation of the sequence of K tables of FIG. 7is completely made out of line, both concerning the first drawing up andthe successive modifications. Afterwards, the testing operator confirmsthe new version that becomes operative in real time, meaning that fromthat moment on, the messages sent to the network shall be generatedstarting from the tables of the last version, without stopping for thisreason the flow of sequential messages. We can therefore conclude thatwhile the compilation phase is completely independent from the flow ofmessages, the deriving updating in the content of messages, coincidingwith the sending of new messages to the network, occurs in synchronousway compared to the frame interval.

From the analysis of information included in the tables of FIG. 7 andrelevant menus, and from the typology of the deriving messages, we candeduce that availing, in whole, or in part, of the M=16 groups ofcarriers relevant to a same time slot, each group including N=8 replicascan be arbitrarily simulated:

-   one or more useful signals;-   one or more isofrequential interferent signals (that in a real    scenario are due to reutilization of the carriers in adjacent    clusters) coming from directions separate from that of the relevant    useful;-   one or more echoes of a useful, and/or interferent signal, (that in    a real scenario are generated by multiple paths) coming from    directions different from that of the useful and/or interferent;-   one or more interferents from adjacent channel, and relevant echoes;    and also the fading effect on each one of the above mentioned    signals, in non-correlated mode compared to the other signals,    through multiplication of beamforming coefficients by a duly    filtered pseudo-noise sequence. The operations concerning this point    are directly performed by CNTR_(—)PC through pre-processing.

The testing system of FIG. 1 is very flexible as for the panorama ofpossible scenarios to simulate, and easy to handle for the testingoperator, whose task is limited to the entering of data in the generaltables of FIG. 7. These advantages derive from the essentially digitalarchitecture of the simulation equipment SIM_(—)RF, which can constructN broad band digital signals at intermediate frequency IF1, . . . , IFN,of the multicarrier type. Each carrier included in the broad bandsignals IF1, . . . , IFN is characterized by a relevant content of theSIM_(—)NCO message, which established the relevant intermediatefrequency; therefore the simulation of several isofrequentialinterferents engages several modules TX_(—)PROC to which SIM_(—)NCOmessages having identical content are sent.

Generalizations

The simulation system of the example lends itself to somegeneralizations that configure the invention applicable to other mobileradio systems with system setting different from the FDMA/TDMA one. Forinstance, as far as the invention is concerned, the TDMA aspect is notstrictly necessary and, strictly speaking, also the FDMA aspect can benot considered, since for the simulation of a minimum, but realisticscenario, one sole carrier is sufficient with its isofrequentialinterferents. As for the invention, if we want to leave out ofconsideration the FDMA/TDMA architecture of the embodiment, we must beconsidered the dynamic characteristic of the simulated scenario which upto now was given by the updating of the significant parameters of thesame at 4.61 ms interval of the GSM frame. This time slot is a goodcompromise between the need to avail of a processing time sufficient tothe generation of configuration messages of the scenario, to theirtransfer on local network, and to the programming of the addressee unitsof the content of the same, and that to be able to simulate a realistictime slot in which the variations indicated by the succession ofparameters, correspond to a same variation of the same magnitudes, butreferred to phenomena which in the real context comprise the involvedcarriers.

From the above we can conclude that it is possible to employ the presentinvention to simulate the radiofrequency scenario in the testing of abase transceiver station of a cellular telephone system of the analoguetype with FDMA philosophy, for instance TACS. In this case, whenever theprocessing times enable it, it is possible to update the scenarioparameters with interval lower than 4.61 ms of the example, reaching afiner accuracy in the dynamic simulation.

From what said up to now we can conclude that, without departing fromthe field of the invention, the same can have further applications, inaddition to those foreseen for cellular telephone systems. For instance,it is possible to use the invention in all the cases where it isnecessary to test receivers for intelligent array antennas employingbeamforming algorithms, but leaving out of consideration the basicphilosophy of all the mobile radio telephone systems, and therefore thefact that all the interferents are caused by the reutilization of thesame carriers in a territory subdivided in cells of adjacent clusters.

Possible applications of the invention in this way could be forecast inthe satellite sector. Other possible applications of the invention insectors different from the mobile radio telecommunication one, could bepredicted in the radar sector.

1. Simulation process of a radiofrequency scenario starting fromgeneration of serial messages including information for obtaining aphase-modulated radiofrequency test signal comprehensive of channelimpairments, including co-channel interference, which is sent to theinput of a receiver under test whose output is monitored, the processcomprising: executing NxP digital modulation of a base band carrier, forobtaining P groups of N base band isofrequential digital replicas ofsaid phase-modulated carrier, P being chosen from 1 to a maximum numberM of modulated carriers fitting an assigned band of the receiver undertest, and N being a number of independent inputs of said receiver;digitally multiplying, for every P groups of N replicas, each base bandreplica by a respective complex constant assigned to the group, thenumerical order of the replicas and the phases of the multiplicativeconstants both increasing gradually in successive products, forbeamforming each of the P groups of N replicas according to a desiredarrival direction of the P groups for simulation; adjusting the powerlevel of each of the P groups of N replicas; digitally multiplying eachbeamformed group of N replicas by a relevant digital intermediatefrequency carrier which carries out frequency conversion of the group ata respective intermediate frequency, thereby establishing for eachintermediate frequency converted beamformed group a relative positioninside the broad band of the receiver under test; summing the Pintermediate frequency converted replicas having the same order in eachbeamformed group, for obtaining N broad band intermediate frequencyreplicas; executing analogue conversion of the N broad band intermediatefrequency replicas and filtering broad band the analogue replicas forreconstruction; executing radiofrequency conversion, amplification andfiltering of the reconstructed analogue replicas for obtaining N broadband radiofrequency replicas constituting a single test signal suitablefor testing the operation of a directional receiver; application of theN broad band radiofrequency replicas directly to N radiofrequency inputsof the receiver under test, each radiofrequency input bypassing anassociated antenna.
 2. Simulation process of radiofrequency scenarioaccording to claim 1, wherein the content of said serial messages isread from general tables of parameters and options defining a scenarioconcerning at least one useful transmission signal and one or moreisofrequential interferent signals, having simulated arrival directionsgenerally different from those of said relevant useful signals. 3.Simulation process according to claim 2, wherein said general tablesconstitute a sequence of K tables cyclically read.
 4. Simulation processaccording to claim 3, wherein operative phases of the simulation processform a sequence repeated at time intervals of the same duration,intermittently using said messages obtained converting a new generaltable of said cyclic sequence, thus giving dynamic and recurrentcharacteristics to said simulated scenario.
 5. Simulation processaccording to claim 4, wherein said equal duration of the time intervalsis such that a variation speed of the contents of said messages issimilar to the one that can be detected in the corresponding saidparameters of a real scenario.
 6. Simulation process according to claim5, wherein said duration is equal to, or lower than 4.61 ms. 7.Simulation process according to claim 4, wherein said general tables areupdated during the testing time, and corresponding updated messages aregenerated in synchronous mode compared to said sequential timeintervals.
 8. Simulation process according to claim 4, furthercomprising an additional acquisition phase of the results of saidtesting, in asynchronous mode compared to said sequential timeintervals.
 9. Simulation process according to claim 2, wherein selectionof some of said options of said general tables involves the compilationof relevant sub-tables containing additional parameters to select forthe selected options.
 10. Simulation process according to claim 4,wherein said carriers are time division multiplexed, and each of saidsequential time intervals of the same duration corresponds to a frametime.
 11. Simulation process according to claim 2, wherein said generaltables also include parameters that take into account the presence ofnoise, a doppler effect due to the speed of mobiles, and the quick andsudden fading of a received electromagnetic field, caused by multiplepaths destructive interference or by masking by obstacles encountered bymobiles in movement.
 12. Testing system of a radiofrequency receiver,including a control processor for generating serial messages directed toorthogonal modulation and frequency conversion devices controlled by thecontent of said messages for generating a phase-modulated radiofrequencytest signal comprehensive of channel impairments, including co-channelinterference which is sent to a receiver under test whose output ismonitored, the testing system comprising: N×P digital modulators of aself-generated base band carrier, for obtaining P groups of N base bandisofrequential digital replicas of said phase-modulated carrier, P beingchosen from 1 to a maximum number M of modulated carriers fitting anassigned band of the receiver under test (DUT), and N being a number ofindependent inputs of said receiver; N×P first digital multipliersarranged for multiplying, for every P groups of N replicas, each baseband replica by a respective complex constant assigned to the group, thenumerical order of the replicas and the phases of the multiplicativeconstants both increasing gradually in successive products, forbeamforming each of the P group of N replicas according to a desiredarrival direction of the P groups for simulation; means for adjusting apower level of each of the P groups of N replicas; N×P second digitalmultipliers for multiplying each beamformed group of N replicas by arelevant digital intermediate frequency carrier which carries outfrequency conversion of the group at a respective intermediatefrequency, so establishing for each intermediate frequency convertedbeamformed group a relative position inside the broad band of thereceiver under test; N digital adding means for summing up all the Pintermediate frequency converted replicas having the same order in eachbeamformed group, for obtaining N broad band intermediate frequencyreplicas; N digital/analogue conversion means of said N broad bandintermediate frequency replicas followed by broad band filtering meansfor reconstructing the analogue replicas; N radiofrequency mixers ofsaid N broad band reconstructed analogue replicas for obtaining N broadband radiofrequency replicas; N radiofrequency amplifiers for amplifyingsaid radiofrequency replicas and orderly sending said amplifiedradiofrequency replicas to N radiofrequency outputs of the testingsystem, where the radiofrequency replicas constitute a single testsignal suitable for testing the operation of a directional receiver; awhole of N coaxial cables, or equivalent means, connecting said Nradiofrequency outputs to a same number of inputs of said receiver,without antenna.
 13. Testing system according to claim 12, wherein theintermediate frequency converted beamformed groups, each of N replicas,are generated by means of P identical digital modules, each including adedicated processor interface communicating with N digital modulators, Nfirst digital multipliers, and N second digital multipliers; the wholedigital modules being connected to N buses for transferring the N broadband intermediate frequency replicas towards as many digital to analogueconverters, through a binary tree of N two-inputs digital adders. 14.Testing system according to claim 12, wherein said control processortransfers to interface means said control messages at sequential timeintervals of identical duration.
 15. Testing system according to claim14, wherein said identical duration of the sequential time intervals issuch that a variation speed of the contents of said messages is similarto that which can be detected in corresponding parameters of a realscenario.
 16. Testing system according to claim 12, wherein saidmessages are obtained from the conversion of general tables ofparameters and options defining a simulated scenario, stored into saidcontrol processor.
 17. Testing system according to claim 16, whereinsaid general tables are organized in a sequence of K tables cyclicallyrepeated.
 18. Testing system according to claim 14, wherein saidduration is equal to or lower than 4.61 ms.
 19. Testing system accordingto claim 16, wherein said general tables are filled in before thetesting and updated during the testing, and the corresponding updatedmessages are generated in synchronous mode compared to said sequentialtime intervals.
 20. Testing system according to claim 14, wherein saidcarriers are time division multiplexed and said duration corresponds toa frame time.
 21. Testing system according to claim 16, wherein saidgeneral tables include also parameters to simulate the presence ofnoise, a doppler effect due to the speed of mobiles, and the quick andsudden fadings of a received electromagnetic field, caused bydestructive interference by multiple paths or by masking by obstaclesencountered by the mobiles in movement.